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Commit a93bf990 authored by Clemens Ladisch's avatar Clemens Ladisch Committed by Jaroslav Kysela
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[ALSA] usb-audio: schedule high speed URBs with 1 ms alignment 



USB generic driver
The EHCI driver doesn't interrupt more than once per millisecond, and
organizes all iso transfers with frame-sized ITDs, so we can (try to)
be more efficient by aligning all URBs on frame boundaries.

Signed-off-by: default avatarClemens Ladisch <clemens@ladisch.de>
parent 71d848ca

sound/usb/usbaudio.c

+14 −6
Original line number Diff line number Diff line
@@ -893,7 +893,7 @@ static int init_substream_urbs(snd_usb_substream_t *subs, unsigned int period_by 
{

	unsigned int maxsize, n, i;

	int is_playback = subs->direction == SNDRV_PCM_STREAM_PLAYBACK;

	unsigned int npacks[MAX_URBS], urb_packs, total_packs;

	unsigned int npacks[MAX_URBS], urb_packs, total_packs, packs_per_ms;



	/* calculate the frequency in 16.16 format */

	if (snd_usb_get_speed(subs->dev) == USB_SPEED_FULL)
@@ -920,14 +920,18 @@ static int init_substream_urbs(snd_usb_substream_t *subs, unsigned int period_by 
	else

		subs->curpacksize = maxsize;



	if (snd_usb_get_speed(subs->dev) == USB_SPEED_HIGH)

		packs_per_ms = 8 >> subs->datainterval;

	else

		packs_per_ms = 1;



	if (is_playback) {

		urb_packs = nrpacks;

		urb_packs = max(urb_packs, (unsigned int)MIN_PACKS_URB);

		urb_packs = min(urb_packs, (unsigned int)MAX_PACKS);

	} else

		urb_packs = 1;

	if (snd_usb_get_speed(subs->dev) == USB_SPEED_HIGH)

		urb_packs = (urb_packs * 8) >> subs->datainterval;

	urb_packs *= packs_per_ms;



	/* allocate a temporary buffer for playback */

	if (is_playback) {
@@ -949,8 +953,12 @@ static int init_substream_urbs(snd_usb_substream_t *subs, unsigned int period_by 
			minsize -= minsize >> 2;

		minsize = max(minsize, 1u);

		total_packs = (period_bytes + minsize - 1) / minsize;

		if (total_packs < 2 * MIN_PACKS_URB)

			total_packs = 2 * MIN_PACKS_URB;

		/* round up to multiple of packs_per_ms */

		total_packs = (total_packs + packs_per_ms - 1)

				& ~(packs_per_ms - 1);

		/* we need at least two URBs for queueing */

		if (total_packs < 2 * MIN_PACKS_URB * packs_per_ms)

			total_packs = 2 * MIN_PACKS_URB * packs_per_ms;

	} else {

		total_packs = MAX_URBS * urb_packs;

	}
@@ -972,7 +980,7 @@ static int init_substream_urbs(snd_usb_substream_t *subs, unsigned int period_by 
		subs->nurbs = 2;

		npacks[0] = (total_packs + 1) / 2;

		npacks[1] = total_packs - npacks[0];

	} else if (npacks[subs->nurbs-1] < MIN_PACKS_URB) {

	} else if (npacks[subs->nurbs-1] < MIN_PACKS_URB * packs_per_ms) {

		/* the last packet is too small.. */

		if (subs->nurbs > 2) {

			/* merge to the first one */